I'm using WMI to gather stats on some of our servers, and I'm trying to get details of the physical disks that are installed in each server.

The servers are various Dell PowerEdge models. Windows' built-in providers is reporting on the RAID volumes and the logical partitions, but I can't find any way to report on what the actual physical drives installed in the server are (presumably because Windows can only see as far as the RAID volumes being presented by the controller, and has no information about what's going on underneath that layer)

Is there a Dell RAID WMI provider I can install for this, or something else I can do to gather these stats?

This does indeed appear to be the only way to get that information, along with the option to run the omreport.exe command. I just check with OpenManage version 6.5, which is still not exposing that information via WMI. There is a way to enumerate all devices with WMI from the DELL server, which includes the HDs, but it gives you no information on them (other than the vendor model id), and you can't reliably filter them out either. Hopefully they will fix this at some point.
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Lucky LukeNov 18 '11 at 14:29

Check out Win32_DiskDrive, Win32_DiskDriveToDiskPartition, Win32_PhysicalMedia (in what I perceive as decreasing usefulness...). I'm on HP servers, so YMMV. (You could also try Win32_LogicalDiskToPartition)

Failing all of this, try ScriptomaticV2 from the Microsoft Scripting Guys to browse WMI.